Systems that rely upon the converse effect, i.e., the conversion of electrical energy to mechanical work, to affect the behavior of the systems may be identified as transductive systems. Bicoupled transductive systems are systems whose actuation mechanisms display both direct, i.e., mechanical work to electrical energy conversion, and converse effects between electrical charge and mechanical work. Such systems employ electromechanical and electromagnetomechanical effects such as ferroelectric/ferroelastic piezoelectric and electrostrictors, magnetostrictors or moving magnetic induction devices such as voice coils. Typically, such devices may be divided into two categories, namely, the ferroelectric/ferroelastic piezoelectric and electrostrictors may be classified as capacitive devices, and the magnetostrictors or magnetic induction devices may be classified as inductive devices.
A principle obstacle to the utilization of converse effect capacitive or inductive devices for transductive systems is the extreme inefficiency and heat dissipation requirements of the electronics to drive these reactive mechanisms. Purely resistive mechanisms, however, can be defined as those for which real and apparent power are substantially the same. In contrast, nearly purely reactive devices such as piezocapacitive or voice coil inductive mechanisms can evince vastly different apparent and real power characteristics. This difference leads to nearly all of the energy that is supplied to the devices being reflected. For linear or hybrid designs, the reflected energy must be damped by thermal dissipation mechanisms, which leads to very inefficient designs, heavy and bulky heat sinking requirements, and high total energy consumption requirements. Accordingly, a new method of driving these reactive mechanisms that avoids the penalties of inefficiency, heat dissipation, energy consumption, and bulk/weight is desired.
Active devices may be utilized to control transductive systems. Active devices or controllers generally comprise a distinct set of sensor circuitry, drive circuitry, and actuator circuitry. In designing an active controller utilizing well known control design methods, each of these distinct circuits is accounted for separately. As a result of treating each of these circuits separately or individually, the effect of the interaction between the electrical, mechanical, and electromechanical characteristics of each of these circuits, as well as the devices to be controlled, is neglected. In addition, well known design techniques require that the sensors and actuators be distinct devices.
Another problem with the conventional control system design approach, in addition to not taking into account the interaction between the electrical, mechanical, and electromechanical effects, is that it provides no mechanism for determining a preferred control structure, actuation authority requirements, or optimal parameter selection. Still another problem is that conventional control systems must incorporate feedback loops external to the drive circuitry and require filtering and or signal conditioning.
A further problem with conventional control systems is the requirement that a sensor measurement system distinct from the actuators be attached to the transductive system. This problem has been partially addressed with the introduction of sensoriactuation and adaptive sensoriactuation designs that utilize both the direct and converse effects. Problems with the sensoriactuation approach are numerous and begin with a circuit design which requires a comparator circuit that a priori assumes an almost exact knowledge of the reactive behavior of the actuators. However, even a simple piezoelectric device attached to a mechanical plate has an imaginary component of impedance that may change drastically from almost purely capacitive to purely inductive. Therefore, such a comparator circuit, in practice, is not useful or amenable to actual operation. In situations where it may be feasible to introduce a comparator circuit, the sensoriactuation system only provides a set of sensed measurements and allows ac commands to be sent to the actuation mechanisms. It provides no insight or method for determining what the ac commands should be. The sensoriactuation approach has no means for delivering a commanded ac voltage or current to the actuation mechanisms without a wholly separate drive amplifier stage. Therefore, there is little in practice to distinguish the ability to derive separate sensor measurements while simultaneously actuating the devices from a conventional control system that utilizes a distinct set of colocated or non-colocated sensors.
In order to solve the above-described problems, a circuit that utilizes a direct measurement of voltage and/or current levels within the drive electronics, which avoids any comparator or pseudo-comparator circuit, and which determines and delivers exactly the required ac voltage or current to a transductive system is needed. What is also required is that such a circuit architecture be readily amenable for re-calibration to effect any alternate state space controller for the system and do so in a way that lends itself to developing the optimal or near optimal selection of commanded ac voltages and/or currents. For many situations, another requirement is that this system consume little or no net energy, have a low thermal signature, and be realizable in a small footprint.
A circuit which attempts to solve these problems has been implemented in a crude fashion by shunted circuit design. However, this approach is restricted to damping vibratory motion passively. For broadband damping, a resistor is shunted across a direct effect mechanism, which is typically a piezocapacitor. For narrow band damping, both an inductor and a resistor must be shunted across the device to form a resonant LRC circuit. This circuit is usually tuned to a resonant frequency of the structure to be damped. In a resistively shunted circuit, the resistor is varied until the circuit time constant is close to the modes to be damped. In resonant shunting, both the inductor and the resistor must be tuned. The primary difficulty with resistive shunted circuits is the requirement of large resistance values to dissipate sufficient energy. However, increasing the resistance results in a decrease in the current flowing through the resistance. It is possible to optimize the resistance value, but it is typically too low to effectively dissipate energy.
More recently, there has been an interest in using RL shunted circuits. However, the large inductance required to tune the electrical resonance near a low frequency structural resonance is unreasonable for passive components. Consequently, active inductors are synthesized using op-amps and other active components such as gyrators to implement piezoelectric vibration absorbers or powered devices. This is sometimes erroneously referred to as "semi-active", although, strictly speaking, semi-active should refer to actively varying a resistance. The problem with using synthetic inductors is that the power op-amps used in synthesizing these inductors are inherently lossy. Thus, all of the aforementioned problems with respect to purely active control, namely, lack of efficiency, energy consumption, bulk/weight, and heat dissipation reappear.
There is a need in the industry for a mechanism that avoids the problem of unwanted energy absorption by capacitive (piezocapacitance) or inductive active mechanisms, and therefore improves energy flow which could be dissipated. However, it is desirable to utilize the increased energy flow more effectively, rather than simply dissipate the energy through a resistor in order to avoid the bandwidth limitations of resonant shunt design and the penalty of having lossy, bulky, and inefficient electronic components needed for synthesizing an inductor, and to improve the overall damping of a system or structure.